There is one cup of heavy cream in the tres leches sauce and and two cups in the mousse.

I hope that clears up the misunderstanding.

Macaroni Grill's Lemon Passion - Jacqueline's Version
Recipe By: Jacqui/recipe-quest
Servings: 9

TRES LECHE:
12 oz Evaporated milk
1 cup Sweetened condensed milk
1 cup Heavy cream
1 tsp Vanilla
1 Tbsp Light rum

CAKE:
1 c. sifted flour
1 Tbsp. baking powder
1/4 c. melted butter
1/2 tsp. lemon extract
1/2 c. milk -- scalded
6 egg yolks
1 c. sugar

MOUSSE:
1 lemon -- zested and juiced
2 tablespoons simple syrup
1 package unflavored gelatin
1 cup heavy cream -- chilled
1 cup lemon curd -- your favorite recipe
2 cups heavy cream
topping
2 cups sweetened whipped cream

Chill the bowl and wire whip of an electric mixer in the freezer.

Whisk together flour and baking powder; keep scalded milk hot. In an electric mixer beat eggs until thick and lemon colored. Gradually beat in sugar and lemon extract. Quickly add flour mixture.
Stir just until mixed. Gently stir in hot milk mixture. Pour
into greased 9 x 9 x 2-inch pan. Bake in 350 degrees oven for 30 to 35 minutes. Cool completely.

While cake is baking combine the ingredients for the tres leche and set
aside.

Remove a slice horizontally from both the top and bottom of the cooled cake. You will want the center slice to be approximately 1/2" thick.
Return the center slice to the baking pan. Save remaining cake for another purpose. Drizzle some of the tres leche sauce over the cake but not so much as to make it soggy.

In a small saucepan combine the lemon juice, 2 tablespoons simple syrup and gelatin. Stir to soften the gelatin. Place over low heat and cook until the gelatin dissolves, stirring constantly. Remove from the heat and pour into a mixing bowl. Remove the bowl and whip from the freezer and add the heavy cream. Whip the cream until soft peaks form. Combine the gelatin mixture, lemon zest and lemon curd. Mix well. Add the lemon mixture to the whipped cream. Continue to beat until the cream forms stiff peaks.

Spread lemon cream over cake and place in the refrigerator to set - 3 to 4 hours.

To serve, pour tres leche sauce on a plate, top with a square of the cake and dollops of the whipped cream. Drizzle with a tiny bit of the sauce.